Ink-jet recording is known as an excellent recording method that is not particularly selective in terms of recording materials (media), and the research and development of recording apparatuses, recording methods, and recording materials have been extensively conducted. Thus, progress in the field of media is particularly significant. From the standpoint of gloss and quality feel, presently available media that has been developed to demonstrate gloss in combination with the increase in absorption rate and absorbed amount of ink are at a level above that of the conventional commercial printing. Media for ink-jet printing can be generally classified into that of a swelling type and that of a porous type, but the media of a porous type that excels in a drying rate of ink has been mainly employed in recent years.
In the mainstream porous-type media, as disclosed in Patent Literatures 1 and 2, an ink absorption layer having pores for taking in the ink is provided on a substrate by using silica or alumina hydrate and, if necessary, a porous gloss layer is provided using colloidal silica or the like. Such specific configuration excels in ink absorbing ability and makes it possible to obtain fine output. Accordingly, it has been advantageously used for consumer photographic applications.
However, the media of this type is very expensive and difficult to manufacture. As a result, the cost thereof is much higher than that of coated paper for general commercial and publishing printing. For this reason, such media has not found significant application in the field of commercial printing where a large output is required to be obtained at a low cost, such as leaflets, catalogues, and pamphlets, regardless of image quality. Significant efforts have heretofore been exerted to reduce the cost of paper, but because a material with a large oil absorption capability (specific surface area) that can maintain high transparency of a layer is usually employed as a filler constituting the ink absorbing layer (receiving layer) of ink-jet media, a special expensive filler such as silica, alumina hydrate, or colloidal silica has to be used, thereby making it very difficult to reduce the cost.
Further, not only in such IJ paper, but also in the media that is made IJ suitable, a cationic additive or a sizing agent is most often used to improve the fixing ability of the colorants and dyes and the pH of the paper surface is brought close to acidic one. Thus, an additive, such as described in Patent Literature 3, is used, cationic fine particles, such as described in Patent Literature 4, are used, and the filler surface is treated with a cationic resin, as described in Patent Literature 5. In most cases, an acidic dye demonstrating anionic properties is used for dye-type ink-jet inks. Because the fixing ability of a dye can be increased by bonding a sulfonic group or the like of an acidic dye with a cationic substance contained in the ink, such technology is presently widely used. Coloring pigments of pigment-type ink-jet inks are also often anionic, and the fixing ability can be improved by the same mechanism. For these reasons, in the case of ink-jet paper, a treatment that decreases the pH of paper surface (shifts it to acidic side) to ensure excellent preservation of ink-jet image is actively conducted, and practically all media designed for ink-jet applications has a pH of the paper surface of 7 or less.
However, inks for commercial printing such as offset printing often employ an oil with a very high boiling point as a solvent and, by contrast with ink-jet inks, the fixation of image after printing is realized by oxidation and polymerization of the solvent.
From the standpoint of fixation, paper with a comparatively fast ink absorption, such as paper for reproduction and copying is preferred. Using a heating roll as a drying aid means for ink-jet printouts is also known, but dye-type oily inks have mainly been suggested, and there are no paper designs for aqueous pigment inks and commercial printing. For example, it has been suggested to improve fixing ability by heating the medium subjected to ink-jet printing from the rear surface to accelerate drying. Drying and fixing can be attained by heating from the rear surface, but with this method the image is not heated directly. As a result, thermal efficiency is very poor in most cases, and although such approach is effective in drying a large amount of moisture contained in the entire media after printing, in most cases it demonstrates practically no effect with respect to a wetting agent (high-boiling solvent) contained in the image. Generally heating at a high temperature of hundred and several tens of degrees is required to dry a high-boiling solvent, the specific temperature depending on the type of the solvent, and such heating is absolutely unacceptable because it causes yellowing and deformation of paper and can burn the paper, as a worst case scenario, and the damage inflicted to the paper cannot be ignored.
In offset printing, fast fixing by drying (oxidation polymerization reaction) is also desired from the standpoint of operability. For this reason, a drying (polymerization) enhancer called “drier” is often added to the ink. Because the drier forms a precipitate of metal ion components under an acidic atmosphere and becomes ineffective, drying ability is known to degrade significantly in the case of paper with a low pH of paper surface such as ink-jet media. In addition, it is well known that wetting water (H water) that is used in offset printing sometimes react with cationic substances of ink-jet media, thereby destroying the hydrophilic-hydrophobic balance of the printing plate and easily causing printing defects such as image contamination. It is also for such technological reasons, rather than only because of cost factors, that the offset printing technology is very difficult to apply to ink-jet media.
Accordingly, an attempt has been made to use an ink-jet ink for printing on a coat paper for commercial printing such as offset printing (Patent Literature 6). However, such paper contains only a small amount of cationic substances that fix dyes, or contain no such substances at all, and the image preservation ability, such as water resistance, after printing is extremely poor, thereby making such paper absolutely unsuitable for practical use.
This is because an SBR latex is generally widely used for the coat layer of a coated paper for commercial printing because of high productivity and low cost thereof. Since the SBR latex uses an anionic emulsifier, it has very poor compatibility with cationic substances such as cationic fixing agents used in ink-jet media. Even if a cationic fixing agent for ink-jet inks is contained in a sufficient amount in a coat paper for printing, the coating liquid is gelled or the SBR emulsion precipitates, thereby making it impossible to obtain the desired printout.
In recent years, ink-jet inks using pigments with excellent water resistance and light resistance surpassing those of dyes as ink colorants have also been employed. Pigments used in such inks are generally identical to those of inks for commercial printing, but such inks are also difficult to use for printing on coated paper for commercial printing that does not take the absorption ability of ink into account. In particular, where high-speed printing is to be performed, bleeding or beading of images occurs and satisfactory images cannot be obtained. Further, it is well known that the images obtained have poor wear resistance, and pigment inks using phthalocyanine blue that has been especially widely used as a cyan colorant are known to be inferior in terms of colorant fixation, specific reasons for such effects being unclear.
For the reasons stated above, it is very difficult to satisfy at the same time the requirements relating to suitability for the conventional offset printing and suitability for ink-jet printing in the field of media for commercial printing having gloss, such as used for catalogues and leaflets, and it is extremely difficult to realize a multipurpose printer suitable for both the offset printing and the ink-jet printing, that is, capable of performing ink-jet printing after offset printing on a coated paper and, conversely; performing offset printing after ink-jet printing.
Patent Literature 7 describes an ink-jet recording ink containing self-dispersible carbon black that has absorbed a water-dispersible polymer compound and is not transmitted in gel filtration chromatography and water, wherein the water-dispersible polymer compound has a gel filtration chromatography transmission ratio equal to or less than 20% when this compound is in a state free from carbon black. Further, the paper recording media in this publication is classified into “usual paper” and “glossy coat paper”, and the “glossy coat paper” is further classified into “semi-glossy paper” and “glossy paper”, and the ink is disclosed to be capable of forming glossy recording images on the “usual paper” that is a medium other than the “glossy coat paper”. However, the ink of Patent Literature 7 is not particularly suitable for “semi-glossy paper”, and the technology described in Patent Literature 7 cannot be considered as a printing method suitable therefor.    [Patent Literature 1] Japanese Patent Application Laid-Open (JP-A) No. 2005-212327    [Patent Literature 2] JP-A No. 11-078225    [Patent Literature 3] Japanese Patent (JP-B) No. 3349803    [Patent Literature 4] JP-A No. 2003-80837    [Patent Literature 5] JP-A No. 2006-321978    [Patent Literature 6] JP-A No. 06-320755    [Patent Literature 7] JP-A No. 2005-163017